Coring tools for managing hydraulic properties of drilling fluid and related methods

ABSTRACT

A coring bit for use on a coring tool for extracting a sample of subterranean formation from a well bore includes a bit body having a cavity, wherein a throat portion of the cavity extends into the bit body from a face of the bit body. The coring bit includes a sleeve disposed within the cavity of the bit body, the sleeve configured to separate a face discharge channel and a throat discharge channel. The face discharge channel is located radially outward of the sleeve and the throat discharge channel is located radially inward of the sleeve. A method of repairing a such a coring includes removing the sleeve from the cavity of a bit body.

FIELD

The present disclosure relates generally to apparatuses and methods fortaking core samples of subterranean formations. More specifically, thepresent disclosure relates to a core bit having features to control flowof drilling fluid into a narrow annulus between the core bit insidediameter and the outside diameter of an associated core shoe of a coringapparatus for reduction of drilling fluid contact with, and potentialinvasion and contamination of, a core being cut.

BACKGROUND

Formation coring is a well-known process in the oil and gas industry. Inconventional coring operations, a core barrel assembly is used to cut acylindrical core from the subterranean formation and to transport thecore to the surface for analysis. Analysis of the core can revealinvaluable data concerning subsurface geological formations—includingparameters such as permeability, porosity, and fluid saturation—that areuseful in the exploration for and production of petroleum, natural gas,and minerals. Such data may also be useful for construction siteevaluation and in quarrying operations.

A conventional core barrel assembly typically includes an outer barrelhaving, at a bottom end, a core bit adapted to cut the cylindrical coreand to receive the core in a central opening, or throat. The opposingend of the outer barrel is attached to the end of a drill string, whichconventionally comprises a plurality of tubular sections that extends tothe surface. Located within, and releasably attached to, the outerbarrel is an inner barrel assembly having an inner tube configured forretaining the core. The inner barrel assembly further includes a coreshoe disposed at one end of the inner tube adjacent the throat of thecore bit. The core shoe is configured to receive the core as it entersthe throat and to guide the core into the inner tube. Both the innertube and core shoe are suspended within the outer barrel with structurepermitting the core bit and outer barrel to rotate freely with respectto the inner tube and core shoe, which may remain substantiallyrotationally stationary. Thus, as the core is cut—by application ofweight to the core bit through the outer barrel and drill string inconjunction with rotation of these components—the core will traverse thethroat of the core bit to eventually reach the core shoe, which acceptsthe core and guides it into the inner tube assembly where the core isretained until transported to the surface for examination.

Conventional core bits are generally comprised of a bit body having anannular face surface on a bottom end. The opposing end of the core bitis configured, e.g., by threads, for connection to the outer barrel.Located at the center of the face surface is the throat, which mayextend into a substantially hollow cylindrical cavity formed in the bitbody. Different types of core bits are known in the industry, such as,by way of non-limiting example, diamond bits, including polycrystallinediamond compact (PDC) bits as well as impregnated bits. In PDC bits, forexample, the face surface typically includes a plurality of cuttersarranged in a selected pattern. The pattern of cutters includes at leastone outside gage cutter disposed near the periphery of the face surfacethat determines the diameter of the bore hole drilled in the formationduring a coring operation. The pattern of cutters also includes at leastone inside gage cutter disposed near the throat that determines theoutside diameter of the core being cut. It is to be understood, however,that the scope of the present disclosure is not limited to PDC bits, butencompasses other core bit types as well.

During coring operations, a drilling fluid is usually circulated throughthe core barrel assembly to lubricate and cool the cutting structure ofthe bit face, such as the plurality of cutters disposed on the facesurface of the core bit, and to remove formation cuttings from the bitface surface to be transported upwardly to the surface through theannulus defined between the drill string and the wall of the well bore.A typical drilling fluid, also termed drilling “mud,” may be ahydrocarbon, a water-based (saltwater or freshwater) or synthetic-basedfluid in which fine-grained mineral matter may be suspended, or anyother fluid suitable to convey the downhole formation cuttings to thesurface. Some core bits include one or more ports or nozzles positionedto deliver drilling fluid to the face surface. Generally, a portincludes a port outlet, or “face discharge outlet,” which may optionallycomprise a nozzle, at the face surface in fluid communication with aface discharge channel. The face discharge channel extends through thebit body and terminates at a face discharge channel inlet. Each facedischarge channel inlet is in fluid communication with an upper annularregion formed between the bit body and the inner tube and core shoe.Drilling fluid received from the drill string under pressure iscirculated into the upper annular region to the face discharge channelinlet of each face discharge channel to draw drilling fluid from theupper annular region. Drilling fluid then flows through each facedischarge channel and discharges at its associated face discharge portto lubricate and cool the plurality of cutters on the face surface andto remove formation cuttings as noted above.

In conventional core barrel assemblies, a narrow annulus exists in theregion between the inside diameter of the bit body and the outsidediameter of the core shoe. The narrow annulus is essentially anextension of the upper annular region and, accordingly, the narrowannulus is in fluid communication with the upper annular region. Thus,in addition to flowing into the face discharge channel inlets, thepressurized drilling fluid circulating into the upper annular regionalso flows into the narrow annulus between the bit body and core shoe,also referred to as a “throat discharge channel.” The location at whichdrilling fluid bypasses the face discharge channel inlets and continuesinto the throat discharge channel may be referred to as the “flowsplit.” The throat discharge channel terminates at the entrance to thecore shoe proximate the face of the core bit and any drilling fluidflowing within its boundaries is exhausted proximate the throat of thecore bit. As a result, drilling fluid flowing from the throat dischargechannel will contact the exterior surface of the core being cut as thecore traverses the throat and enters the core shoe.

Conventional core barrel assemblies are prone to damage core samples invarious ways during operation. For example, core barrel assemblies maybe prone to damage core samples by exposing the core to the flow ofdrilling fluid, particularly if the flow velocity is relatively high andthe area of exposure is large. For example, a throat discharge channelthrough which drilling fluid is discharged with high velocity in theregion where the core is exposed to the drilling fluid can createsignificant problems during coring operations, especially when coring inrelatively soft to medium hard formations, or in unconsolidatedformations. Drilling fluids discharged from the throat discharge channelenter an unprotected interval where no structure stands between suchdrilling fluids and the outer surface of the core as the core traversesthe throat and enters the core shoe. Such drilling fluid can also invadeand contaminate the core itself. For soft or unconsolidated formations,these drilling fluids invading the core may wash away, or otherwiseseverely disturb, the material of the core. The core may be so badlydamaged by the drilling fluid invasion that standard tests forpermeability, porosity, and other characteristics produce unreliableresults, or cannot be performed at all. The severity of the negativeimpact of the drilling fluid on the core increases with the velocity ofthe drilling fluid in the unprotected interval. Fluid invasion ofunconsolidated or fragmented cores is a matter of great concern in thepetroleum industry as many hydrocarbon-producing formations, such assand and limestone, are of the unconsolidated type. For harderformations, drilling fluid coming into contact with the core may stillpenetrate the core, contaminating the core and making it difficult toobtain reliable test data. Thus, limiting fluid invasion of the core cangreatly improve core quality and recoverability while yielding a morereliable characterization of the drilled formation.

The problems associated with fluid invasion of core samples describedabove may be a result, at least in part, of the material comprising thebit body of a core barrel assembly. Conventional core bits oftencomprise hard particulate materials (e.g., tungsten carbide) dispersedin a metal matrix (commonly referred to as “metal matrix bits”). Metalmatrix bits have a highly robust design and construction necessitated bythe severe mechanical and chemical environments in which the core bitmust operate. However, the dimensional tolerances of metal matrix corebits (including inner surface diameter, gap width of the throatdischarge channel, TFA of the face discharge channels and depth of thejunk slots) are limited by the strength of the metal matrix material. Insuch metal matrix core bits, portions of the bit body must exceed aminimal thickness necessary to maintain structural integrity and inhibitthe formation of cracks or microfractures therein.

BRIEF SUMMARY

In some embodiments, a coring bit for use on a coring tool forextracting a sample of subterranean formation from a well bore includesa bit body having a cavity, wherein a throat portion of the cavityextends into the bit body from a face of the bit body. The coring toolalso includes a sleeve disposed within the cavity of the bit body. Thesleeve is configured to separate at least one face discharge channel anda throat discharge channel. The at least one face discharge channel islocated radially outward of the sleeve and the throat discharge channelis located radially inward of the sleeve.

In other embodiments, a method of repairing a coring tool for extractinga sample of subterranean formation from a well bore includes removing asleeve from a cavity of a bit body of the coring tool. The sleeve isconfigured to separate at least one face discharge channel and a throatdischarge channel during operation of the coring tool. The at least oneface discharge channel is located radially outward of the sleeve and thethroat discharge channel is located radially inward of the sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

While the disclosure concludes with claims particularly pointing out anddistinctly claiming specific embodiments, various features andadvantages of embodiments of the disclosure may be more readilyascertained from the following description when read in conjunction withthe accompanying drawings, in which:

FIG. 1 illustrates a side, partially cut away plan view of a core barrelassembly for cutting a core sample from a subterranean formation.

FIG. 2 illustrates a bottom, face view of a core bit of the core barrelassembly of FIG. 1.

FIG. 3A illustrates a longitudinal cross-sectional view of the core bitand associated core shoe of FIGS. 1 and 2, taken along line of FIG. 2,including a sleeve affixed to the core bit, according to an embodimentof the present disclosure.

FIG. 3B illustrates a longitudinal cross-sectional view of sleeve havinga fluid passage extending therethrough, according to an embodiment ofthe present disclosure.

FIG. 3C illustrates a longitudinal cross-sectional view of sleeve havinga fluid passage extending therethrough, according to an additionalembodiment of the present disclosure.

FIG. 4 illustrates a partial longitudinal cross-sectional view of thecore bit and associated core shoe of FIG. 3A.

FIG. 5A illustrates a lateral cross-sectional view of a sleeve havingthree (3) separate sections, according to an embodiment of the presentdisclosure.

FIG. 5B illustrates a lateral cross-sectional view of a sleeve havingtwo (2) separate sections, according to an embodiment of the presentdisclosure.

FIG. 6 illustrates a lateral cross-sectional view of the core bit andassociated sleeve and core shoe of FIGS. 3A and 4, taken along lineVI-VI of FIG. 3A.

FIG. 7 illustrates a partial, magnified lateral cross-sectional view ofthe core bit and associated sleeve of FIG. 6.

FIG. 8A illustrates a partial longitudinal cross-sectional view of acore bit and associated sleeve and core shoe, wherein the throatdischarge channel includes a change in total flow area, according to anembodiment of the present disclosure.

FIG. 8B illustrates a partial longitudinal cross-sectional view of acore bit and associated sleeve and core shoe, wherein the sleeveincludes recesses formed in an inner surface thereof, according to anembodiment of the present disclosure.

FIG. 9 illustrates a longitudinal cross-sectional view of a sleeveconfigured similar to the sleeve of FIG. 8B, wherein the sleeve hasrecesses that are rectangular in shape when viewed in a longitudinalcross-sectional plane and extend annularly about a circumference of aninner surface of the sleeve.

FIG. 10 illustrates a longitudinal cross-sectional view of a sleeveconfigured similar to the sleeve of FIG. 8B, wherein the recesses extendin a helical pattern about a circumference of the inner surface of thesleeve.

FIG. 11 illustrates a longitudinal cross-sectional view of a sleeveconfigured similar to the sleeve of FIG. 8B, wherein the recesses arearcuate in shape, when viewed in a longitudinal cross-sectional plane.

FIG. 12 illustrates a longitudinal cross-sectional view of a sleeveconfigured similar to the sleeve of FIG. 11, wherein the recesses extendin a helical pattern about a circumference of the inner surface of thesleeve.

FIG. 13 illustrates a perspective view of a section of a sleeve havinglongitudinal recesses formed in an inner surface thereof, according toan embodiment of the present disclosure.

FIG. 14 illustrates a perspective view of a section of a sleeve havinglongitudinal recess segments formed in an inner surface thereof,according to an embodiment of the present disclosure.

FIG. 15 illustrates a perspective view of a section of a sleeve havingcircular recesses formed in an inner surface thereof, according to anembodiment of the present disclosure.

FIG. 16 illustrates a perspective view of a section of a sleeve havingan array of rectangular pockets formed in an inner surface thereof,according to an embodiment of the present disclosure.

FIG. 17 illustrates a partial longitudinal cross-sectional view of acore bit and associated sleeve and core shoe, wherein the inner surfaceof the sleeve and the outer surface of the core shoe include variationsin diameter in the direction of fluid flow therethrough, according to anembodiment of the present disclosure.

FIG. 18 illustrates a partial longitudinal cross-sectional view of acore bit and associated core shoe, wherein an integral portion of thebit body is located radially between face discharge channels and athroat discharge channel of the core bit, according to an embodiment ofthe present disclosure.

FIG. 19 illustrates a partial longitudinal cross-sectional view of acore bit and associated sleeve and core shoe, wherein the sleeve and anintegral portion of the bit body are located radially between facedischarge channels and a throat discharge channel of the core bit,according to an embodiment of the present disclosure.

FIG. 20 illustrates a longitudinal cross-sectional view of a core bit,with a partial cross-sectional view of an associated core shoe andsleeve superimposed thereon, wherein the core bit includes an annular,ring-shaped face discharge channel, according to an additionalembodiment of the present disclosure.

FIG. 21 illustrates a lateral cross-sectional view of the core bit andassociated sleeve and core shoe of FIG. 20, taken along line XXI-XXI ofFIG. 20

FIG. 22 illustrates a lateral cross-section view of a core bit andassociated sleeve and core shoe, wherein the face discharge channel hasan outer surface substantially following the outer surface of the bitbody, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual views ofany particular core bit, shoe, or sleeve of a coring tool, or componentthereof, but are merely idealized representations employed to describeillustrative embodiments. Thus, the drawings are not necessarily toscale.

The cited references cited herein, regardless of how characterized, arenot admitted as prior art relative to the disclosure of the subjectmatter claimed herein.

As used herein, directional terms, such as “above”; “below”; “up”;“down”; “upward”; “downward”; “top”; “bottom”; “top-most”;“bottom-most”; “proximal” and “distal” are to be interpreted from areference point of the object so described as such object is located ina vertical well bore, regardless of the actual orientation of the objectso described. For example, the terms “above”; “up”; “upward”; “top”;“top-most” and “proximal” are synonymous with the term “uphole,” as suchterm is understood in the art of subterranean well bore drilling.Similarly, the terms “below”; “down”; “downward”; “bottom”;“bottom-most” and “distal” are synonymous with the term “downhole,” assuch term is understood in the art of subterranean well bore drilling.

As used herein, the term “longitudinal” refers to a direction parallelto a longitudinal axis of the core barrel assembly. For example, a“longitudinal” cross-section shall mean a “cross-section viewed in aplane extending along the longitudinal axis of the core barrelassembly”.

As used herein, the terms “lateral”; “laterally”; “transverse” or“transversely” shall mean “transverse to a longitudinal axis of the corebarrel assembly.” For example, a “lateral” or “transverse” cross-sectionshall mean a cross-section viewed in a plane transverse to thelongitudinal axis of the core barrel assembly.

Disclosed herein are embodiments of a core barrel assembly withincreased effectiveness at reducing the exposure of the core sample todrilling fluid during a coring operation. Decreasing the amount and/orvelocity of drilling fluid contacting the core sample may beaccomplished by decreasing hydraulic losses, such as fluid flowresistance (also termed “head loss” or “resistance head”) within theface discharge channels and increasing hydraulic losses within thethroat discharge channel. Hydraulic losses of the various channels areat least partly a function of the Total Flow Area (TFA) along thosechannels. Thus, as set forth more fully in the embodiments disclosedbelow, the hydraulic losses of the face discharge channels may bereduced by increasing the TFA of the face discharge channels, while thehydraulic losses of the throat discharge channel may be increased byreducing the TFA or otherwise increasing the fluid flow resistance ofthe throat discharge channel. Reducing the hydraulic losses of the facedischarge channels or increasing the hydraulic losses of the throatdischarge channel may both result in an increase in drilling fluid beingdiverted from the throat discharge channel and instead flowing throughthe face discharge channels and away from the core. Such management ofthe hydraulic losses of the face discharge channels and the throatdischarge channel may also reduce the velocity of drilling fluid exitingthe throat discharge channel relative to prior art core bits. Themaximum TFA of the face discharge channels is limited by the radialspace of the bit body and the need to maintain minimum wall thicknesseswithin the bit body to prevent cracks or microfractures from formingtherein. Additionally, the minimum TFA of the throat discharge channelis limited because a sufficient radial gap between an inner surface ofthe core bit and an outer surface of the core shoe is necessary to allowthe core bit to rotate with respect to the core shoe without catching orbinding therewith. Embodiments of a core barrel assembly that optimizefluid management therein by increasing the TFA of the face dischargechannels and/or decreasing the TFA of the throat discharge channeland/or increasing flow restriction within the throat discharge channelare set forth below. The embodiments disclosed herein also improve themanufacturability and reparability of core bits.

FIG. 1 illustrates a core barrel assembly 2. The core barrel assembly 2may include an outer barrel 4 having a core bit 6 disposed at a bottomend thereof. An upper end 8 of the outer barrel 4 opposite the core bit6 may be configured for attachment to a drill string (not shown). Thecore bit 6 includes a bit body 10 having a face surface 12. The facesurface 12 of the core bit 6 may define a central opening, or throat 14,that extends into the bit body 10 and is adapted to receive a core (notshown) being cut.

The bit body 10 may comprise steel or a steel alloy, including amaraging steel alloy (i.e., an alloy comprising iron alloyed with nickeland secondary alloying elements such as aluminum, titanium and niobium),and may be formed at least in part as further set forth in U.S. PatentPublication No. 2013/0146366 A1, published Jun. 6, 2013, to Cheng et al.(hereinafter “Cheng”), the disclosure of which is incorporated herein inits entirety by this reference. In other embodiments, the bit body 10may be an enhanced metal matrix bit body, such as, for example, apressed and sintered metal matrix bit body as disclosed in one or moreof U.S. Pat. No. 7,776,256, issued Aug. 17, 2010, to Smith et al. andU.S. Pat. No. 7,802,495, issued Sep. 28, 2010, to Oxford et al., thedisclosure of each of which is incorporated herein in its entirety bythis reference. Such an enhanced metal matrix bit body may comprise hardparticles (e.g., ceramics such as oxides, nitrides, carbides, andborides) embedded within a continuous metal alloy matrix phasecomprising a relatively high strength metal alloy (e.g., an alloy basedon one or more of iron, nickel, cobalt, and titanium). As a non-limitingexample, such an enhanced metal matrix bit body may comprise tungstencarbide particles embedded within an iron, cobalt, or nickel basedalloy. As a further non-liming example, such an enhanced metal matrixbit body may comprise a ceramic metal composite material includingceramic particles disposed in a continuous metal matrix. However, it isto be appreciated that the bit body 10 may comprise other materials aswell, and any bit body material is within the scope of the embodimentsdisclosed herein, including materials formed by rapid prototypingprocesses.

Removably disposed inside the outer barrel 4 may be an inner barrelassembly 16. The inner barrel assembly 16 may include an inner tube 18adapted to receive and retain a core for subsequent transportation tothe surface. The inner barrel assembly 16 may further include a coreshoe (not shown in FIG. 1) that may be disposed proximate the throat 14for receiving the core and guiding the core into the inner tube 18. Thecore shoe is discussed in more detail below. The core barrel assembly 2may include other features not shown or described with reference to FIG.1, which have been omitted for clarity and ease of understanding.Therefore, it is to be understood that the core barrel assembly 2 mayinclude many features in addition to those shown in FIG. 1.

FIGS. 2-4, 6 and 7 show additional views of the core bit 6 depicted inFIG. 1, according to various embodiments disclosed herein. FIG. 2 is abottom view of the core bit 6; FIGS. 3 and 4 show longitudinalcross-sectional views of the core bit 6, as taken along line III-III ofFIG. 2; FIG. 6 shows a lateral cross-sectional view of the core bit 6,as taken along line VI-VI of FIG. 3A; and FIG. 7 shows a magnifiedportion of the lateral cross-sectional view of FIG. 6.

As can be seen in FIG. 2, the throat 14 may open into the bit body 10 atthe face surface 12. The bit body 10 may include a plurality of blades20 at the face surface 12. A plurality of cutters 22 may be attached tothe blades 20 and arranged in a selected pattern. The pattern of cutters22 (shown longitudinally and rotationally superimposed one upon anotheralong the bit profile in FIG. 2 and FIG. 3A, respectively) may includeat least one outside gage cutter 24 that determines the diameter of thebore hole cut in the formation. The pattern of cutters 22 may alsoinclude at least one inside gage cutter 26 that determines the diameterof the core 28 (shown by the dashed line) being cut and entering thethroat 14. Radially extending fluid passages 30 may be formed on theface surface 12 between successive blades 20, which fluid passages 30are contiguous with associated junk slots 31 on the gage of the core bit6 between the blades 20. The face surfaces of the fluid passages 30 maybe recessed relative to the blades 20. The bit body 10 may furtherinclude one or more face discharge outlets 32 for delivering drillingfluid to the face surface 12 to lubricate the cutters 22 during a coringoperation.

Referring to FIG. 3A, each face discharge outlet 32 is in fluidcommunication with a face discharge channel 34 extending from the facedischarge outlet 32 through the bit body 10 and inwardly terminating ata face discharge channel inlet 36. The bit body 10 may at leastpartially define or limit one or more face discharge channels 34extending through the bit body 10 from associated face discharge channelinlets 36 to associated face discharge outlets 32 at the face surface 12of the bit body 10. The face discharge channels 34 may becircumferentially spaced. However, in other embodiments, the bit body 10may at least partially define as few as only one (1) annular facedischarge channel 34 extending through the bit body 10 from a facedischarge channel inlet 36 to the face surface 12 of the bit body 10.The bit body 10 may have an inner cavity 38 extending longitudinallytherethrough and bounded by an inner surface 40 of the bit body 10. Thecavity 38 may optionally be substantially cylindrical. The throat 14opens into the cavity 38. At least a portion of at least one of the facedischarge channels 34 may be defined or limited by at least a portion ofthe inner surface 40 of the bit body 10. The inner tube 18 may extendinto the inner cavity 38 of the bit body 10. A core shoe 42 may bedisposed at the lower end of the inner tube 18 and may be at leastpartially disposed within at least a portion of the bit body 10. Asshown, the core shoe 42 may be a separate body coupled to the inner tube18. However, in other embodiments, the core shoe 42 and the inner tube18 may be integrally formed together. The inner tube 18 and the coreshoe 42 may each be in the form of a tubular body, and each may besuspended so that the core bit 6 and the outer barrel 4 may freelyrotate about the inner tube 18 and the core shoe 42. The core shoe 42may have a central bore 44 configured and located to receive the core 28therein as the core 28 traverses the throat 14 and to guide the core 28into the inner tube 18. The core shoe 42 may be hardfaced to increaseits durability.

A core catcher 46 may be carried by the core shoe 42 and may be housedwithin the central bore 44 of the core shoe 42. The core catcher 46 maycomprise, for example, a wedging collet structure located within thecore shoe 42. The core catcher 46 may be sized and shaped to enable thecore 28 to pass through the core catcher 46 when travelinglongitudinally upward into the inner tube 18. When the core barrelassembly 2 begins to back out of the well bore, the outer surface ofwedge-shaped portion 48 of the core catcher 46 comprising a number ofcircumferentially spaced collet fingers may interact with a taperedportion 50 of an inner surface 51 of the core shoe 42 to cause thecollet fingers to constrict around and frictionally engage with the core28, reducing (e.g., eliminating) the likelihood that the core 28 willexit the inner tube 18 after it has entered therein and enabling thecore 28 to be fractured under tension from the formation from which thecore 28 has been cut. The core 28 may then be retained in the inner tube18 until the core 28 is transported to the surface for analysis. It isto be appreciated, however, that a core catcher is an optional featureof this disclosure and if a core catcher is used in conjunction with thedisclosure it can be any type of core catcher known in the industry,such as but not limited to a spring-type catcher, collet catcher, flapcatcher, full closure catcher, or any other appropriate catcher typeknown in the art. The catcher must at least partly interact with partsof the coring tool such as but not limited to the core shoe, the bit, abit shank (not shown) to allow for catching the core when the coringtool is drawn.

An annular region 52 of the core barrel assembly 2 is located betweenthe inner surface 40 of the bit body 10 and outer surfaces 54, 56 of thecore shoe 42 and the inner tube 18, respectively. The annular region 52forms a drilling fluid flow path extending longitudinally through thecore barrel assembly 2 from a proximal end of the bit body 10 to theface discharge channel inlets 36. During a coring operation, drillingfluid is circulated under pressure into the annular region 52 such thatdrilling fluid can flow therefrom to the face surface 12 of the core bit10, as described in more detail below. A flow diversion sleeve 60 may bedisposed within the bit body 10. As shown in FIG. 3A, the sleeve 60 maybe rigidly affixed to the inner surface 40 of the bit body 10. Thesleeve 60 may have a radially inner surface 61 and a radially outersurface 62 extending from a longitudinal upper end 63, or “proximalend,” of the sleeve 60 to a longitudinal bottom end 64, or “distal end,”of the sleeve 60. The face discharge channels 34 may be located radiallyoutward from the outer surface 62 of the sleeve 60. The upper end 63 ofthe sleeve 60 may define a portion of the face discharge channel inlets36. In other embodiments, as shown in FIG. 3B, a portion of the upperend 63 of the sleeve 60 may abut a shoulder portion of the inner surface40 of the bit body 10 and the sleeve 60 may define one or more fluidpassages 65 a extending through a portion of the sleeve 60 from theupper end 63 of the sleeve 60 to an associated face discharge channel34. In yet other embodiments, as shown in FIG. 3C, one or more fluidpassages 65 b may extend laterally through an intermediate portion ofthe sleeve 60 to allow the fluid to flow from the inner cavity 38 to theface discharge channels 34. Referring to FIG. 3A, disposed proximate theupper end 63 of the sleeve 60 is an annular reservoir 66 between theadjacent inner surface 40 of the bit body 10 and the outer surface 54 ofthe core shoe 42. The annular region 52 and the annular reservoir 66 maybe continuous with one another without any substantial flow restrictionstherebetween. However, in other embodiments, the annular region 52 andthe annular reservoir 66 may be distinct, separate annular regions,wherein the annular reservoir 66 is located below the annular region 52.For example, in such alternative embodiments, the annular region 52 andthe annular reservoir 66 may be separated from one another by a portionof the bit body 10 extending radially inward in a manner to restrictflow between the annular region 52 and the annular reservoir 66.

With continued reference to FIG. 3A, a narrow annulus 68, also referredto as a “throat discharge channel,” may be positioned longitudinallydownward from the upper end 63 of the sleeve 60 and radially between theinner surface 61 of the sleeve 60 and the outer surface 54 of the coreshoe 42. Drilling fluid circulating into the annular region 52 collectsin the annular reservoir 66. In the embodiment of FIG. 3A, when thedrilling fluid approaches the upper end 63 of the sleeve 60, the upperend 63 of the sleeve 60 splits the flow, with some drilling fluidflowing into the face discharge channel inlets 36 for deliver to theface surface 12 through the face discharge channels 34, while theremainder of the drilling fluid flows through the throat dischargechannel 68 and exits through the throat 14. Thus, the upper end 63 ofthe sleeve 60 may be effectively termed a “flow split” in thisembodiment. However, it is to be appreciated that, in other embodiments,the flow split may occur at other longitudinal locations. For example,in FIG. 3C, the flow split may occur at the fluid passages 65 bextending through the intermediate portion of the sleeve 60. Withcontinued reference to FIG. 3A, the throat discharge channel 68 mayextend longitudinally from the flow split to the throat 14 of the bitbody 10. The throat discharge channel 68 may also be said to extendlongitudinally from the face discharge channel inlets 36 to the throat14 of the bit body 10. The throat discharge channel 68 is essentially asmaller volume extension of, and in fluid communication with, theannular region 52. The throat discharge channel 68 includes a boundaryprofile 70 that defines the shape of the flow path in the throatdischarge channel 68. Each inlet 36 may be oriented at an angle 69 toincrease the hydrodynamic efficiency of the flow split, inducing moredrilling fluid to bypass the throat discharge channel 68 and enter theface discharge channels 34. The inlets 36, the face discharge channels34 and the throat discharge channel 68 may be configured to managehydraulic losses therein to divert more drilling fluid through the facedischarge channels 34, as described in more detail below.

A first portion 42 a of the core shoe 42 may substantially surround thewedge-shaped portion 48 of the core catcher 46. The first portion 42 aof the core shoe 42 may be located longitudinally between a secondportion 42 b and a third portion 42 c of the core shoe 42, wherein thesecond portion 42 b is located longitudinally below the first portion 42a and extends toward the face surface 12 of the core bit 6, with thethird portion 42 c located longitudinally above the first portion 42 a.Because the first portion 42 a of the core shoe 42 may at leastpartially surround the wedge-shaped portion 48 of the core catcher 46,an outer surface 54 a of the first portion 42 a may have a diametergreater than a diameter of an outer surface 54 b of the second portion42 b and a diameter of an outer surface 54 c of the third portion 42 cof the core shoe 42; however, it is to be appreciated that the diameterof the outer surface 54 a of the first portion 42 a may be substantiallyequivalent to the diameter of the outer surface 54 c of the thirdportion in other embodiments. Because the second portion 42 b of thecore shoe 42 may have a diameter less than that of the first portion 42a of the core shoe 42, the second portion 42 b may be termed a “narrow”portion of the core shoe relative to the first portion 42 a thereof.

The flow split may be located at the second, narrow portion 42 b of thecore shoe 42. Accordingly, the outer surface 54 b of the second portion42 b of the core shoe 42 may define at least a portion of the throatdischarge channel 68. Such a portion of the throat discharge channel 68may be located radially inward from at least a portion of the innersurface 61 of the sleeve 60. Furthermore, such a portion of the throatdischarge channel 68 may be defined by at least a portion of the innersurface 61 of the sleeve 60. The flow split may be located at the narrowportion 42 b of the core shoe 42 to provide more radial space for thethroat discharge channel 68, the face discharge channels 34, and theregions of the bit body 10 surrounding these channels to maintainminimum wall thicknesses throughout the bit body 10 to prevent cracks ormicrofractures from forming in the bit body 10 during use. The minimumwall thickness of various portions of the bit body 10 necessary toprevent cracks or microfractures from forming therein depends uponnumerous factors, including, by way of non-limiting example, materialcomposition and design of the bit body 10, the method(s) of forming thebit body 10, the subterranean formation material in which the bit body10 is used, and other operational constraints. In other embodiments (notshown), the flow split may be longitudinally located at the firstportion 42 a or the third portion 42 c of the core shoe 42. Furthermore,in yet other embodiments (not shown), the diameter of the core shoe 42may be substantially constant along the entire length of the core shoe42.

Referring to FIG. 4, drilling fluid entering the throat dischargechannel 68 will flow therethrough past a distal, lower-most end 72 ofthe core shoe 42 and exit the throat discharge channel 68 through thethroat 14. The sleeve 60 may surround at least a lower portion of thecore shoe 42. A longitudinal interval L₁ measured from the lower-mostend 72 of the core shoe to a longitudinal midpoint of the inside gagecutter 26 may be termed an “unprotected interval” of the throat 14because, once the drilling fluid has passed the lower-most end 72 of thecore shoe 42, no structure stands between the drilling fluid and thecore sample 28. Thus, in the unprotected interval L₁, drilling fluidexiting the throat discharge channel 68 may contact, and thereby invadeand contaminate, the core sample 28 as the core 28 traverses the throat14 and enters the core shoe 42.

The sleeve 60 may be rigidly attached to an inner surface 40 of the bitbody 10. The sleeve 60 may comprise an erosion-resistant material suchas, by way of non-limiting example, cemented tungsten carbide. Thebottom end 64 of the sleeve 60 may be beveled and may be affixed to amating portion 76 of the inner surface 40 of the bit body 10. In theembodiment of FIG. 4, the bottom end 64 of the sleeve 60 and the matingportion 76 of the bit body 10 are each shown as having correspondingbeveled surfaces; however, it is to be appreciated that the bottom end64 of the sleeve 60 and the mating portion 76 of the bit body 10 mayhave other configurations as well. With continued reference to FIG. 4,the outer surface 62 of the sleeve 60 may also be attached to portionsof the inner surface 40 of the bit body 10 located circumferentiallybetween adjacent face discharge channels 34. The sleeve 60 may beattached to the inner surface 40 of the bit body 10 by one or more ofbrazing, shrink fitting, adhesives, welding, or suitable mechanicalfastening features. The sleeve 60 may also include a torque transmittingfeature, such as circumferentially spaced keys extending into like-sizedand spaced recesses in the inner surface 40 of the bit body 10,configured to prevent loosening of the sleeve 60 relative to the bitbody 10, as may occur responsive to heat and/or friction experienced bythe sleeve 60 or the bit body 10 adjacent the sleeve 60. The innersurface 61 of the sleeve 60 may define at least a portion of theboundary profile 70 of the throat discharge channel 68. Additionally,the outer surface 62 of the sleeve 60 may define at least a portion ofthe face discharge channels 34. As shown in FIG. 4, the sleeve 60 mayform a barrier between the throat discharge channel 68 and the facedischarge channels 34.

The outer surface 62 of the sleeve 60 may have a diameter less than adiameter of all portions of the inner surface 40 of the bit body 10longitudinally upward of the longitudinal position at which the sleeve60 is to be attached to the bit body 10 so that the sleeve 60 may beslid into place as a single, unitary body within the inner cavity 38during assembly of the sleeve 60 within the bit body 10. Once the sleeve60 is inserted into its final position where the bottom end 64 of thesleeve 60 abuts the mating portion 76 of the inner surface 40 of the bitbody 10, the sleeve 60 may be rigidly affixed to the inner surface 40 ofthe bit body, as previously described.

In other embodiments (not shown), the outer surface 62 of the sleeve 60may have a diameter greater than a diameter of at least a portion (i.e.,a “narrow” portion) of the inner surface 40 of the bit body 10longitudinally upward of the longitudinal position at which the sleeve60 is to be attached to the bit body 10. In such embodiments, the sleeve60 may comprise two or more separate circumferential sections, such asthe three separate circumferential sections 60 a, 60 b, 60 c shown inFIG. 5A or the two separate circumferential sections 60 d, 60 e shown inFIG. 5B. Referring to FIG. 5A, each of the three separatecircumferential sections 60 a, 60 b, 60 c may have a maximum lateraldimension less than the diameter of the narrow portion of the innersurface 40 of the bit body 10. In such embodiments, the separatecircumferential sections 60 a, 60 b, 60 c may be individually insertedthrough the cavity 38 in the bit body 10 until each has cleared thenarrow portion, and may subsequently be individually rigidly affixed tothe inner surface 40 of the bit body 10 in their final positions to formthe sleeve 60. In other embodiments, such as shown in FIG. 5B, theseparate circumferential sections 60 d, 60 e may be temporaryelastically deformed during the insertion to pass through the narrowportion. In the embodiments of FIGS. 5A and 5B, the separatecircumferential sections 60 a-60 e of the sleeve 60 may be individuallyrigidly affixed to the inner surface 40 of the bit body 10 by brazing,adhesives, or mechanical fastening features. Alternatively, the separatecircumferential sections 60 a-60 e of the sleeve 60 may be fittedtogether to form the sleeve 60 after they have cleared the narrowportion of the inner surface 40 of the bit body 10, and may subsequentlybe rigidly attached to the inner surface 40 of the bit body 10, aspreviously described. In still other embodiments, the sleeve 60 may notbe affixed to the inner surface 40 of the bit body 10 and may be looselyheld in place by the limited installation space within the bit body 10.

The sleeve 60 may be configured to be replaceable. For example, if thesleeve 60 becomes damaged or worn during use, or if access is needed tothe face discharge channels 34 or associated inlets 36, the sleeve 60may be detached from the bit body 10. In embodiments where the outersurface 62 of the sleeve 60 has a diameter less than a diameter of allportions of the inner surface 40 of the bit body 10 longitudinallyupward of the longitudinal position at which the sleeve 60 is to beattached to the bit body 10, the sleeve 60 may be removed as a singlebody. Alternatively, the sleeve 60 may be separated into smaller piecesprior to its removal from the cavity 38 of the bit body 10. Inembodiments where the outer surface 62 of the sleeve 60 has a diametergreater than a diameter of a narrow portion of the inner surface 40 ofthe bit body 10 located longitudinally upward of the longitudinalposition at which the sleeve 60 is to be attached to the bit body 10,such as shown in FIG. 5A, the sleeve 60 may be separated into itsseparate circumferential sections 60 a, 60 b, 60 c prior to its removalfrom the cavity 38 of the bit body 10. The separate circumferentialsections may be temporarily elastically deformed during the removal topass through the narrow portion. The sleeve 60 may be destructivelyseparated into smaller pieces prior to removal in such embodiments aswell. After the sleeve 60 has been removed, the sleeve 60 may berepaired, modified or reconfigured and subsequently reinserted andreattached to the inner surface 40 of the bit body 10, as previouslydescribed. In other embodiments, a replacement sleeve may be insertedinto the bit body 10 in the same manner as previously described for thesleeve 60. It is to be appreciated that the replacement sleeve may beidentical to the sleeve 60 or may have at least one feature differentthan that of the sleeve 60, as discussed in more detail below.

FIG. 6 illustrates a lateral cross-sectional view of the core bit 6 ofFIGS. 1-4, taken along line VI-VI of FIG. 3A. The outer surface 62 ofthe sleeve 60 may define at least a portion of a radially inward surface78 of some or all of the face discharge channels 34. The remainingsurfaces 80 of the face discharge channels 34, which may be termed“radially outer surfaces,” may be formed in the inner surface 40 of thebit body 10 to form, together with the outer surface 62 of the sleeve60, the face discharge channels 34. Each of the face discharge channels34 may have a non-circular shape, such as, for example, a generallyelliptical shape, when viewed in a plane transverse to the direction offluid flow through the face discharge channels 34, such as the lateralcross-sectional plane illustrated in FIG. 6. In other embodiments, eachof the face discharge channels 34 may have a generally rectangular shapewhen viewed in a lateral cross-sectional plane. It is to be appreciatedthat the face discharge channels 34 may have other shapes when viewed ina lateral cross-sectional plane. It is also to be appreciated that atleast one of the face discharge channels 34 may have a shape andcross-sectional area different than a shape of at least one other facedischarge channel 34, when viewed in a lateral cross-sectional plane,and that the shape and/or the position of one or more of the facedischarge channel 34 cross sections may vary along the longitudinalaxis. By way of non-limiting example, a portion of about 40% or more ofthe longitudinal length of the at least one face discharge channel 34may have a non-circular cross-sectional shape and the remaining portionmay have a circular cross-sectional shape. The face discharge channels34 may terminate at associated face discharge outlets 32, which may havelateral, cross-sectional shapes similar to those of the face dischargechannels 34, or as shown in FIG. 1, may each be of a conventional,circular shape. Optionally, the face discharge outlets 32 and/or theface discharge channels 34 may include nozzles.

The face discharge channels 34 may be formed prior to attachment of thesleeve 60 to the bit body 10. Thus, in the absence of the sleeve 60, theface discharge channel inlets 36 and the radially outer surfaces 80 ofthe face discharge channels 34 may be machined into the bit body 10 atleast partially from the cavity 38 of the bit body 10 (enabling theformation of face discharge channels 34 having non-circular shapes whenviewed in a lateral cross-sectional plane) via machining methods, suchas cutting, milling, grinding, eroding, abrading or other formationmethods, such as casting, centrifugal casting, additive manufacturing or3D printing. For example, an entire longitudinal extent of the facedischarge channels 34, extending from the associated inlets 36 toassociated outlets 32 at the face surface 12 of the bit body 10, may beformed in the bit body 10 from the cavity 38 of the bit body 10.However, in other embodiments, a portion less than an entirelongitudinal extent of the face discharge channels 34 may be formed inthe bit body 10 from the cavity 38 of the bit body 10.

FIG. 7 illustrates a magnified view of the core bit 10 and associatedsleeve of FIG. 6. Because the face discharge channels 34 may be formedin the bit body 10 to have non-circular shapes when viewed in a lateralcross-sectional plane, the TFA of the face discharge channels 34 may bemaximized by encompassing more of the circumferential space of the bitbody 10. Such a configuration reduces the hydraulic losses within theface discharge channels 34, resulting in more drilling fluid bypassingthe throat discharge channel 68 and instead flowing through the facedischarge channels 34 and away from the core sample 28. The facedischarge channels 34 may each have a maximum circumferential dimensionC₁ greater than a maximum radial dimension W₁. The maximum radialdimension W₁ of the face discharge channels 34 may be maximized suchthat a minimum radial distance W₂, measured between a radiallyoutward-most location of the outer surface 80 of the face dischargechannels 34 and the radial inward-most surface 31 a of the junk slots31, approaches a minimum bit body 10 wall thickness required to resistformation of cracks or microfractures therein. Furthermore, thenon-circular shape of the face discharge channels 34 allows the maximumcircumferential dimension C₁ of each face discharge channel 34 to bemaximized such that a minimum circumferential distance C₂ betweenadjacent face discharge channels 34 approaches the minimum bit body 10wall thickness required to resist formation of cracks or microfracturestherein. The sum of the maximum circumferential dimensions C₁ of theface discharge channels 34 may subtend an angle of at least about 50degrees about a longitudinal axis L of the bit body 10 in a planetransverse to the longitudinal axis of the bit body 10. In otherembodiments, the sum of the maximum circumferential dimensions C₁ of theface discharge channels 34 may subtend an angle between about 70 degreesand about 145 degrees about the longitudinal axis L of the bit body 10.In yet other embodiments, the sum of the maximum circumferentialdimensions C₁ of the face discharge channels 34 may subtend an anglegreater than about 145 degrees about the longitudinal axis L of the bitbody 10. It is to be appreciated that the aforementioned planetransverse to the longitudinal axis of the bit body 10 is locatedlongitudinally downward of the face discharge channel inlets 36, suchthat the angle subtended by the maximum circumferential dimensions C₁ ofthe face discharge channels 34 does not include the face dischargechannel inlets 36. Additionally, one or more of the inner and outersurfaces 61, 62 of the sleeve and the radially outer surfaces 80 of theface discharge channels 34 may be coated with a coating to reduce theeffects of friction between such surfaces and the drilling fluid and/orto reduce the effects of erosion of the drilling fluid on such surfaces.By way of non-limiting example, one or more of the inner and outersurfaces 61, 62 of the sleeve and the radially outer surfaces 80 of theface discharge channels 34 may have a layer of hardfacing materialapplied by a spray coating or a galvanic application, and may be heattreated or mechanically treated, such as by blasting or by hardeningprocesses.

Additionally, the absence of the sleeve 60 during formation of the facedischarge channel inlets 36 may allow easier access to the inlets 36 tobe shaped non-cylindrically and/or have a varying diameter along alength thereof. For example, the face discharge channel inlets 36,similar to the face discharge channels 34 previously described inreference to FIG. 7, may have a maximum circumferential dimensiongreater than a maximum radial dimension to maximize the TFA of the facedischarge channel inlets 36.

Additionally, because the sleeve 60 is replaceable and may be removedfrom the inner surface 40 of the bit body 10 after use, therebyproviding access to the face discharge channels 34 from the cavity 38 ofthe bit body 10, the face discharge channels 34 and the associatedinlets 36 may be repaired or otherwise modified after the core bit 6 hasbeen used. For example, the face discharge channels 34 may be furtherprocessed and/or machined to reduce the surface friction of the surfacesthereof, to increase the TFA thereof, to change the transversecross-sectional shape thereof, or to apply an erosion-resistant and/orfriction-resistant coating to the surfaces thereof. The inlets 36 may bemachined and or processed in a similar manner. Additionally, the inlets36 may be machined to adjust the angle of approach of the inlets 36.Thus, the hydrodynamic efficiency of any of the flow split, the facedischarge channels 34, and the throat discharge channel 68 may berepaired and/or improved after the core barrel assembly 2 has been used.Furthermore, while the replacement sleeve subsequently affixed to theinner surface 40 of the bit body 10 may be substantially identical tothe original sleeve 60, in other embodiments, the replacement sleeve maydiffer from the original sleeve 60 in one or more properties, including,by way of non-limiting example, material composition, radial thickness,configuration of the upper end 63 forming part of the face dischargechannel inlets 34, or surface features, such as those disclosed in moredetail below. Thus, properties of the face discharge channels 34, thethroat discharge channel 68, and the face discharge channel inlets 36may be adjusted merely by replacing the sleeve 60. The choice of thesleeve 60 properties may be based on the experience with the sleeve thatis to be replaced or the formation that was engaged or that is expectedto be engaged downhole.

FIGS. 8A and 8B illustrate a partial longitudinal cross-section view ofa core bit 6 and associated sleeve 60 and core shoe 42 according toadditional embodiments of the present disclosure. At least a portion ofone or more of the outer surface 54 b of the core shoe 42 and the innersurface 61 of the sleeve 60 defining the throat discharge channel 68 mayfurther define a single TFA change or a series of consecutive TFAchanges, also termed “stages,” in the throat discharge channel 68. Eachstage of the series of consecutive TFA changes in the throat dischargechannel 68 may have a TFA, measured in a plane transverse to the generaldirection of fluid flow through the throat discharge channel 68,different than that of the immediately preceding and/or immediatelysucceeding stages in the general direction of fluid flow through thethroat discharge channel 68. As shown in FIG. 8A, the throat dischargechannel 68 may include a single stage, represented by a dashed circle75, separating a first region 77 a from a second, lower region 77 b ofthe throat discharge channel 68. The stage 75 may be defined by thecontour of the inner surface 61 of the sleeve 60 and the outer surface54 of the core shoe 42 within the throat discharge channel 68.Optionally, a radial width R₁ of the throat discharge channel 68 withinthe first region 77 a may be less than a radial width R₂ within thesecond region 77 b of the throat discharge channel 68. In this manner,the narrower radial width R₁ of the first region may restrict the flowof drilling fluid entering the throat discharge channel 68 and divertdrilling fluid into the face discharge channels 34, while the widerradial width R₂ of the second region 77 b of the throat dischargechannel may provide an increase in TFA within the second region 77 b,thereby reducing the velocity of drilling fluid flowing through andexiting the second region 77 b and into the unprotected interval L₁,thus reducing damage to the core sample 28.

In the embodiment shown in FIG. 8B, the series of consecutive TFAchanges may be in the form of a plurality of recesses 86 formed in theinner surface 61 of the sleeve 60. A TFA of the throat discharge channel68 within the recesses 86 is greater than a TFA of the throat dischargechannel 68 outside of the recesses 86. Each of the recesses 86 may beformed to extend annularly at least partly about a circumference of theinner surface 61 of the sleeve 60. However, it is to be understood thatthe recesses 86 may take other forms, shapes and configurations and maybe combined with, or replaced by, recesses in the opposing outer surfaceof the core shoe 42, as described in more detail below. The recesses 86may have a radial depth predetermined according to a number of factors,including, by way of non-limiting example, desired flow characteristicsof drilling fluid through the throat discharge channel 68, materialcomposition of the sleeve 60 and the radial wall thickness of the sleeve60 between the inner and outer surfaces 61, 62 thereof. Additionally,the radial width of the throat discharge channel 68, measured from bothinside and outside the recesses 86, may be tailored according to anumber of factors, including, by way of non-limiting example, thecomposition, viscosity, density, a dispersion parameter, and/or thequality of the drilling fluid and rotational velocity of the core bit 6.

With continued reference to FIG. 8B, drilling fluid diverted into thethroat discharge channel 68 will encounter the stages as it flowstherethrough. For example, the drilling fluid will encounter stages atwhich the TFA therein increases (within the recesses 86) and decreases(between adjacent recesses 86). The consecutive stages also have theeffect of inducing swirl in the drilling fluid and thus increasing thetortuosity and length of the flow path taken by the drilling fluid as itflows through the throat discharge channel 68. These effects increasethe flow resistance within the throat discharge channel 68. Therefore,as the number of recesses 86 and/or the degree of difference in TFAbetween each stage is increased, the flow resistance across the throatdischarge channel 68 is also increased. As the flow resistance acrossthe throat discharge channel 68 is increased, the more the drillingfluid is restricted within the throat discharge channel 68, decreasingthe amount of drilling fluid flowing into the throat discharge channel68 while increasing the amount of drilling fluid flowing into the facedischarge channels 34. In this manner, the amount of drilling fluidcontacting the core 28 may be reduced. Moreover, this increased flowresistance across the throat discharge channel 68 may be accomplishedwhile providing increased radial width of the throat discharge channel68 over prior art coring bits, reducing the likelihood that particulatesor debris within the drilling fluid become lodged between the outerdiameter 54 of the core shoe 42 and the inner surface 61 of the sleeve60 within the throat discharge channel 68 in a manner to causerotational friction between the bit body 10 and the core shoe 42, orworse, rotationally bind the core bit 6 to the core shoe 42 so that thecore bit 6 cannot rotate relative to the core shoe 42, thus causingfailure of the core barrel assembly 2.

FIGS. 9-12 illustrate cross-sectional views of various embodiments ofthe sleeve 60. As shown in FIG. 9, the recesses 86 formed in the innersurface 61 of the sleeve 60 may have a rectangular shape when viewed ina longitudinal cross-sectional plane. The recesses 86 may extend in anannular pattern about a circumference of the inner surface 61 of thesleeve 60. Alternatively, as shown in FIG. 10, the recesses 86 mayextend in a helical pattern about the inner surface 61 of the sleeve 60.In other embodiments, as shown in FIG. 11, the recesses 86 formed in theinner surface 61 of the sleeve 60 may have an arcuate shape when viewedin a longitudinal cross-sectional plane. In yet other embodiments, therecesses 86 may have other shapes when viewed in a longitudinalcross-sectional plane. FIG. 12 illustrates recesses 86 having an arcuateshape in a longitudinal cross-sectional plane and extending in a helicalpattern about the inner surface 61 of the sleeve 60.

It is to be appreciated that FIGS. 8A-12 illustrate a limited number ofexamples of recesses 86 that may be employed to provide consecutivechanges in TFA in the throat discharge channel 68. In other embodiments,the recesses 86 may have other shapes when viewed in a longitudinalcross-sectional plane. Additionally, recesses 86 may be formed in theouter surface 54 b of the core shoe 42 in the throat discharge channel68. In yet other embodiments, recesses 86 may be formed in the outersurface 54 b of the core shoe 42 and the inner surface 61 of the sleeve60 within the throat discharge channel 68. In further embodiments, therecesses 86 may be in the form of circumferentially extending channels86 a, as shown in FIG. 13. In additional embodiments, the recesses 86may be in the form of circumferentially extending channel segments 86 b,as shown in FIG. 14. In other embodiments, the recesses 86 may be in theform of an array of circular pockets 86 c, as shown in FIG. 15. In yetother embodiments, the recesses 86 may be in the form of an array ofskewed rectangular pockets 86 d, as shown in FIG. 16. It is to beappreciated that the shape, form, orientation and/or configuration ofthe recesses 86 is not limited by this disclosure.

Furthermore, in other embodiments, the series of consecutive TFA changesmay be provided by forming a plurality of protrusions extending radiallyinward from the inner surface 61 of the sleeve 60 and/or radiallyoutward from the outer surface 54 b of the core shoe 42 in the throatdischarge channel 68. Such protrusions may be effectively configured asan inverse of any of the “recesses” 86-86 d previously described, andmay have other configurations as well. In yet other embodiments, theseries of consecutive TFA changes may include a combination of recesses86 and protrusions formed on or in the inner surface 61 of the sleeve 60and/or the outer surface 54 b of the core shoe 42 in the throatdischarge channel 68. Additionally, at least one of the recesses 86and/or protrusions may vary in shape, form, orientation and/orconfiguration from at least one other recess 86 and/or protrusion.

It is to be appreciated that the throat discharge channel 68 may includeany number of TFA changes provided by recesses 86 and/or protrusionsformed on and/or in the inner surface 61 of the sleeve 60 and the outersurface 54 b of the core shoe 42 located within the throat dischargechannel 68. For example, in the embodiment shown in FIG. 8B, the throatdischarge channel 68 has at least twenty-two (22) TFA changes thereincaused by the presence of eleven (11) recesses 86 formed in the innersurface 61 of the sleeve 60. However, in other embodiments, otherquantities of TFA changes may be appropriate or better suited for thethroat discharge channel 68. It is to be appreciated that the maximumnumber of TFA changes in the throat discharge channel is virtuallyunlimited.

FIG. 17 illustrates an additional embodiment of a series of theconsecutive TFA changes designed to increase flow resistance through thethroat discharge channel 68. The throat discharge channel 68 boundaryprofile 70 includes two (2) stages, indicated by dashed circles 90, atwhich the outer surface 54 b of the second portion 42 of the core shoe42 and the inner surface 61 of the sleeve 60 decrease in diameter in thedirection of fluid flow. It is to be appreciated, however, thatvirtually any number of such stages may be included. These stages 90force the drilling fluid to increase its flow path and create, in someinstances, swirl as the drilling fluid flows through each stage 90relative to a similar flow path without any such stages. These factorsincrease the hydraulic losses in the throat discharge channel 68 byincreasing the flow resistance encountered by the drilling fluidtherein, thus restricting fluid flow within the throat discharge channel68 and increasing fluid flow diverted through the face dischargechannels 34, as previously described. Additionally, at least parts ofthe inner surface 61 of the sleeve 60 or the outer surface 54 of thecore shoe 42 may be coated with a coating to increase the frictionbetween the drilling fluid and at least one of sleeve 60 and the coreshoe 42 and thereby increase the hydraulic losses within the fluid.

It is to be appreciated that, while FIGS. 3-8B and 17 illustrate asleeve 60 located radially between the face discharge channels 34 andthe throat discharge channel 68, in other embodiments, the sleeve 60 maybe omitted. In such embodiments, as shown in FIG. 18, the radial andlongitudinal space occupied by the sleeve 60 in other embodiments mayinstead be occupied by an integral portion 92 of the bit body 10. Theintegral portion 92 of the bit body 10 may have a generally cylindricalconfiguration. A longitudinal upper-most end 94 of the integral portion92 of the bit body 10 may define a portion of the face discharge channelinlets 36. An inner surface 96 of the integral portion 92 of the bitbody 10 may define a radially outer surface of the throat dischargechannel, and may be located radially inward of the face dischargechannels 34. The inner surface 96 of the integral portion 92 of the bitbody 10 and the outer surface 54 of the core shoe 42 may additionallyinclude features for restricting flow of drilling fluid within thethroat discharge channel 68, including all the features disclosed inrelation to FIGS. 8A-17. For example, the inner surface 96 of theintegral portion 92 and/or the outer surface 54 of the core shoe 42 inthe throat discharge channel 68 may include recesses formed thereinand/or protrusions formed thereon to restrict drilling fluid in thethroat discharge channel 68, as previously described. Additionally, thethroat discharge channel 68 boundary profile may include one or morestages at which the outer surface 54 of the core shoe 42 and the innersurface 96 of the integral portion 92 abruptly decrease in diameter inthe direction of fluid flow to restrict flow of drilling fluid in thethroat discharge channel 68, as previously described. In furtherembodiments, as shown in FIG. 19, a sleeve 60 and an integral portion 92of the bit body 10 may be located between the face discharge channels 34and the throat discharge channel 68. In such an embodiment, the integralportion 92 of the bit body 10 may be less than fully circumferential.For example, in such an embodiment, the integral portion 92 of the bitbody 10 may be in the form of one or more guide blocks, as furtherdescribed below.

In embodiments where the sleeve 60 is omitted, the face dischargechannels 34 and the associated inlets 36, may be formed to havenon-circular shapes in a transverse cross-sectional plane in a manneralternative to being machined from the cavity 38 of the bit body 10. Byway of non-limiting example, for metal bit bodies, such as steel bitbodies, the bit body may be formed by a centrifugal die casting process,as set forth in U.S. Patent Publication No. 2013/0146366 A1, publishedJun. 6, 2013, to Cheng et al. In such processes, metal material may beintroduced into a die that defines the shape of the bit body to beformed, including the face discharge channels and associated inlets 36.The die is heated and rotated to generate centrifugal forces on theheated metal to cause the metal to conform to the die shape. The die issubsequently cooled, and the formed bit body is removed from the die.Alternatively, for steel bit bodies, the face discharge channels havingnon-circular shapes in a lateral plane may be machined from the facesurface 12 of the bit body 10. For metal-matrix bit bodies, which may beextremely difficult, if not virtually impossible, to machine in apractical sense, the bit body having face discharge channels withnon-circular shapes in a lateral cross-sectional plane may be formed byplacing hard particulate material, such as tungsten carbide, within agraphite mold and infiltrated with a binder, such as a copper alloy, asalso set forth in Cheng. Cast resin-coated sand, graphite displacementsor, in some instances, tungsten carbide particles in a flexiblepolymeric binder, may be employed to define topographic features of thebit. A machinable blank or blanks may be disposed within the bit mold todefine the finished shape of the face discharge channels 34 and 36inlets thereof prior to infiltration of the hard particulate material.Such blanks may comprise graphite, steel, or other materials. Afterhardening of the infiltrant, the blank may be machined away, leaving theface discharge channels 34 and associated 36 inlets shaped as desired.Other methods of forming the non-circular shaped face discharge channels34 and associated inlets 36 are also possible in embodiments omittingthe sleeve 60. It is to be appreciated that such additional formingmethods may be utilized to form bit bodies 10 in embodiments where thesleeve 60 is included, in additional to embodiments where the sleeve isomitted.

FIGS. 20-22 illustrate a core bit 6, sleeve 60 and an associated coreshoe 42, wherein the core bit 6 has a single, annular, ring-shaped facedischarge channel, according to additional embodiments of the presentdisclosure.

FIG. 20 illustrates superimposed longitudinal cross-sectional views ofsuch a bit body 10 with and without the associated sleeve 60 and coreshoe 42 disposed in the cavity 38 of the bit body 10. The bit body 10and the sleeve 60 of FIG. 20 may be configured similarly to those ofFIGS. 1-7; therefore, like components are represented by like referencenumbers. The bit body 10 may have an inner cavity 38 extendinglongitudinally therethrough and bounded by an inner surface 40 of thebit body 10. The cavity 38 may be substantially cylindrical, althoughother configurations are within the scope of the present disclosure. Thecavity 38 of the bit body 10 may be configured to receive a core shoe 42therein. A single face discharge channel 134 may have an annular shapein a lateral plane and may extend from an inlet 136 of the facedischarge channel 134 to a plurality of face discharge outlets 132. Anannular reservoir 66 may be located longitudinally upward of the facedischarge channel inlet 136 and radially between the inner surface 40 ofthe bit body 10 and the outer surface 54 of the core shoe 42. Drillingfluid circulating into the annular region 52 collects in the annularreservoir 66, where the drilling fluid can feed into the face dischargechannel inlet 136 or the throat discharge channel 68 for delivery to theface surface 12.

A proximal portion of the face discharge channel inlet 136 may belocated at a first longitudinal location P₁ longitudinally downward ofthe first portion 42 a of the core shoe 42 housing the core catcher 46.A diameter of the inner surface 40 of the bit body 10 may graduallyincrease in a longitudinal direction toward the face surface 12 of thebit body 10 to a second longitudinal location P₂, beyond which extends aregion 150 of the bit body 10 where the diameter of the inner surface 40of the bit body 10 remains substantially constant. The radially outerpart of the region 150 of the bit body 10 forms the radially outer partof the annular, ring shaped face discharge channel 134. The annular,ring-shaped discharge channel 134 effectively terminates at a thirdlongitudinal location P₃ proximate the face surface 12 of the bit body10. The outer contour of the annular, ring-shaped face discharge channel134 may be formed prior to attachment of the sleeve 60 to the bit body10. Thus, in the absence of the sleeve 60, the annular, ring-shaped facedischarge channel 134 may be machined into the bit body 10 at leastpartially from the cavity 38 of the bit body 10 via machining methods,such as cutting, milling, turning, grinding, electrochemical machining,eroding, abrading or other formation methods, such as casting,centrifugal casting, additive manufacturing or 3D printing.

A mating portion 76 of the inner surface 40 of the bit body 10 may belocated proximate the third longitudinal location P₃ and may beconfigured to receive the bottom end 64 of the sleeve 60, as previouslydescribed. The bottom end 64 of the sleeve 60 may be rigidly attached tothe mating portion 76 of the inner surface 40 of the bit body 10 by oneor more of brazing, shrink fitting, adhesives, or mechanical fasteningfeatures, as previously described. The sleeve 60 may also include atorque transmitting feature, such as circumferentially spaced keys onthe bottom end 64 of the sleeve 60 extending into like-sized and spacedrecesses in the mating portion 76 of the inner surface 40 of the bitbody 10. Likewise, torque transmitting elements may be included into theouter surface 62 of the sleeve 60. The sleeve 60 may form a barrierbetween the annular, ring-shaped discharge channel 134 located radiallyoutward of the sleeve 60 and the throat discharge channel 68 locatedradially inward of the sleeve 60, as previously described. A radiallyinner surface 61 of the sleeve 60 may define at least a portion of aboundary profile 70 of the throat discharge channel 68. Additionally, aradially outer surface 62 of the sleeve 60 may define a radially innersurface 178 of the annular, ring-shaped face discharge channel 134. Alongitudinal upper-most end 63 of the sleeve 60 may at least partiallydefine the inlet 136 of the face discharge channel 134. In otherembodiments, the sleeve 60 may include fluid passages extendingtherethrough, as previously described, allowing drilling fluid to flowthrough the sleeve 60 and into the ring-shaped face discharge channel134.

The outer surface 62 of the sleeve 60 may have a diameter less than adiameter of all portions of the inner surface 40 of the bit body 10longitudinally upward of the second longitudinal location of the bitbody 10 so that the sleeve 60 may be slid into place as a single,unitary body within the cavity 38 during assembly of the sleeve 60within the bit body 10. Alternatively, the outer surface 62 of thesleeve 60 may have a diameter greater than a diameter of at least aportion of the inner surface 40 of the bit body 10 longitudinally upwardof the second longitudinal location P₂ of the bit body 10. In suchembodiments, the sleeve 60 may comprise two or more separatecircumferential sections that may be assembled in the bit body 10 anddisassembled therefrom, as previously described in relation to FIG. 5.Optionally, the sleeve 60 may be loosely maintained in place between thecore shoe 42, the bit body 10, and the mating portion 76 of the innersurface of the bit body, wherein the sleeve 60 may be held in place bythe downward flow of drilling fluid during operation. With continuedreference to FIG. 20, once the sleeve 60 is inserted into its finalposition, the sleeve 60 may be rigidly affixed to the inner surface 40of the bit body, as previously described. Furthermore, the sleeve 60 maybe configured to be replaceable, as previously described.

The annular, ring-shaped face discharge channel 134 may be in fluidcommunication with the face discharge outlets 132. The face dischargeoutlets 132 may be milled or bored from the face surface 12 of the bitbody 10 until the face discharge outlets 132 intercept the annular,ring-shaped face discharge channel 134. It is to be appreciated that theface discharge outlets 132 may be formed by other methods, such ascutting, grinding, casting, centrifugal casting, additive manufacturing,3D printing, or powder metallurgical methods. The face discharge outlets132 may intercept the face discharge channel 134 at an angle, as shownin FIG. 20, or may extend from the face surface 12 at a directionparallel with the longitudinal axis L of the bit body 10. The facedischarge outlets 132 may each be of a conventional, circular shape andoptionally include nozzles. In other embodiments, the face dischargeoutlets 132 have other non-circular shapes in a lateral plane.

With continued reference to FIG. 20, to facilitate accurate insertion ofthe sleeve 60 through the cavity 38 of the bit body 10 and into placesuch that the end surface 64 of the sleeve 60 abuts the mating portion76 of the inner surface 40 of the bit body 10, one or more guide blocks160 may optionally be affixed to the inner surface 40 of the bit body 10at one (1) or more circumferential locations between the second andthird longitudinal locations P₂, P₃ of the bit body 10. In additionalembodiments, the one (1) or more guide blocks may be helical-shaped. Inaddition to guiding the sleeve 60 into place during insertion, the guideblocks 160 may also stabilize the sleeve 60 during insertion andoperation. One or more recesses (not shown) may be formed in the outersurface of the sleeve 60 and/or into one or more of the guide blocks 160to guide and stabilize the sleeve 60 during insertion and operation.Each of the optional guide blocks 160 may have an inner surface 162conforming to the outer surface 62 of the sleeve 60 and may have aradius, measured from the longitudinal axis L of the bit body 10,equivalent to or slightly less than the radius of the outer surface 62of the sleeve 60, measured from the longitudinal axis L of the bit body10. The optional guide blocks 160 may be coated with a coating to reducethe effects of friction between the guide blocks 160 and the drillingfluid and/or reduce the effects of erosion of the drilling fluid on thesurfaces thereof. The optional guide blocks 160 may be affixed to theinner surface 40 of the bit body 10 by one or more of brazing, shrinkfitting, adhesives, mechanical fastening features, or any other suitablemeans or method as known in the art. In other embodiments, the optionalguide blocks 160 may be formed into the inner surface 40 of the bit body10. In such embodiments, the inner surface 40 of the bit body 10 betweenthe second and third longitudinal locations P₂, P₃ may be machined, fromthe cavity 38 of the bit body 10, removing material therefrom in amanner leaving the optional guide blocks 160 extending radially inwardfrom the inner surface 40 of the bit body 10.

FIG. 21 illustrates a lateral cross-sectional view of the core barrelassembly of FIG. 20, taken along line XXI-XXI of FIG. 20. The outersurface 62 of the sleeve 60 may define the radially inward surface ofthe annular, ring-shaped face discharge channel 134. Optional guideblocks 160 may extend radially inward from the inner surface 40 of thebit body 10, as previously disclosed. It is to be appreciated that whileFIG. 21 illustrates three (3) guide blocks 160 evenly spaced about thecircumference of the inner surface 40 of the bit body 10, more or lessthan three (3) guide blocks 160 may be included, and the guide blocks160 may be unevenly spaced about the circumference of the inner surface40 of the bit body 10. As depicted, the annular, ring-shaped facedischarge channel 134 may be sized to maximize the radial andcircumferential dimensions thereof while maintaining necessary wallthicknesses within the bit body 10, including between the face dischargechannel 134 and the radial inward-most surface 31 a of the junk slots 31to resist formation of cracks or microfractures therein. In additionalembodiments, as shown in FIG. 22, a radially outer surface 180 of theface discharge channel 134 may generally conform with an outer surface185 of the bit body 10. In such embodiments, the radially outer surface180 of the annular, ring-shaped face discharge channel 134 may extendradially into the blades 20. Such embodiments optimize the radial spaceof the bit body 10 for enhanced hydraulic performance of the core barrelassembly 2 to divert drilling fluid away from the core sample.

It is to be appreciated that the sleeves 60 and or the core shoes 42 ofFIGS. 20-22 may additionally include features for restricting flow ofdrilling fluid within the throat discharge channel 68, including all thefeatures disclosed in relation to FIGS. 8-17. For example, the innersurface 61 of the sleeve 60 and/or the outer surface 54 b of the secondportion 42 b of the core shoe 42 in the throat discharge channel 68 mayinclude recesses formed therein and/or protrusions formed thereon torestrict drilling fluid in the throat discharge channel 68, aspreviously described. Additionally, the throat discharge channel 68boundary profile 70 may include one or more stages at which the outersurface 54 b of the second portion 42 of the core shoe 42 and the innersurface 61 of the sleeve 60 abruptly decrease in diameter in thedirection of fluid flow to restrict flow of drilling fluid in the throatdischarge channel 68, as previously described. In further embodiments,at least portions of the inner surface 61 of the sleeve 60 or the outersurface 54 of the core shoe 42 may be coated with a coating to increasethe friction between drilling fluid and at least one of the sleeve 60and the core shoe 42 and thereby increase the hydraulic losses withinthe fluid.

The various embodiments of the core bit 6 previously described mayinclude many other features not shown in the figures or described inrelation thereto, as some aspects of the core bit 6 may have beenomitted from the text and figures for clarity and ease of understanding.Therefore, it is to be understood that the core bit 6 may include manyfeatures in addition to those shown in the figures. Furthermore, it isto be further understood that the core bit 6 may not contain all of thefeatures herein described.

Additional, nonlimiting embodiments within the scope of this disclosureinclude:

Embodiment 1: A coring bit for use on a coring tool for extracting asample of subterranean formation from a well bore, comprising: a bitbody having a cavity, wherein a throat portion of the cavity extendsinto the bit body from a face of the bit body; and a sleeve disposedwithin the cavity of the bit body, the sleeve configured to separate atleast one face discharge channel and a throat discharge channel, the atleast one face discharge channel located radially outward of the sleeve,the throat discharge channel located radially inward of the sleeve.

Embodiment 2: The coring bit of Embodiment 1, further comprising acoring shoe disposed in the cavity of the bit body.

Embodiment 3: The coring bit of Embodiment 1 or Embodiment 2, whereinthe sleeve comprises two or more parts.

Embodiment 4: The coring bit of any one of Embodiments 1 through 3,wherein the sleeve defines at least one recess in a radially innersurface of the sleeve, the at least one recess providing the throatdischarge channel with zones of higher and lower flow resistance.

Embodiment 5: The coring bit of any one of Embodiments 1 through 4,wherein the throat discharge channel comprises a first region and asecond region, wherein the second region has a total flow area higherthan a total flow area of the first region.

Embodiment 6: The coring bit of any one of Embodiments 1 through 5,further comprising one or more guide blocks affixed to an inner surfaceof the bit body within the cavity, the one or more guide blocksconfigured to guide the sleeve into place during insertion of the sleeveinto the cavity of the bit body or to support the sleeve duringoperation of the coring bit.

Embodiment 7: The coring bit of any one of Embodiments 1 through 6,wherein the sleeve defines one or more fluid passages extending throughthe sleeve.

Embodiment 8: The coring bit of any one of Embodiments 1 through 7,wherein at least a portion of a length of the at least one facedischarge channel has non-circular cross-sectional shape.

Embodiment 9: The coring bit of Embodiment 8, wherein the portion of thelength of the at least one face discharge channel having a non-circularcross-sectional shape comprises about 40% or more of the length of theat least one face discharge channel.

Embodiment 10: The coring bit of Embodiment 8 or Embodiment 9, wherein atotal circumferential dimension of the portion of the at least one facedischarge channel subtends an angle of at least about 72 degrees about alongitudinal axis of the bit body in a plane transverse to thelongitudinal axis of the bit body 10.

Embodiment 11: The coring bit of any one of Embodiments 8 through 10,wherein a total circumferential dimension of the portion of the at leastone face discharge channel subtends an angle of at least about 108degrees about a longitudinal axis of the bit body in a plane transverseto the longitudinal axis of the bit body 10.

Embodiment 12: The coring bit of any one of Embodiments 8 through 11,wherein a total circumferential dimension of the portion of the at leastone face discharge channel subtends an angle of at least about 144degrees about a longitudinal axis of the bit body in a plane transverseto the longitudinal axis of the bit body 10.

Embodiment 13: A method of repairing a coring tool for extracting asample of subterranean formation from a well bore, the methodcomprising: removing a sleeve from a cavity of a bit body of the coringtool, the sleeve configured to separate at least one face dischargechannel and a throat discharge channel during operation of the coringtool, the at least one face discharge channel located radially outwardof the sleeve, the throat discharge channel located radially inward ofthe sleeve.

Embodiment 14: The method of Embodiment 13, further comprising:repairing a radially outer surface of the at least one face dischargechannel after removing the sleeve; and installing a replacement sleeveinto the cavity of the bit body, wherein the replacement sleeve is oneof the removed sleeve, a repaired sleeve, and a new sleeve.

Embodiment 15: The method of Embodiment 14, wherein repairing theradially outer surface of the at least one face discharge channelcomprises forming at least a portion of the at least one face dischargechannel by one or more of a cutting, milling, turning, grinding,eroding, polishing, additive manufacturing, 3D printing, and castingprocess.

Embodiment 16: The method of any one of Embodiments 13 through 15,wherein the sleeve comprises two or more parts.

Embodiment 17: The method of any one of Embodiments 14 through 16,further comprising installing at least one guide block in the cavity ofthe bit body prior to installing the replacement sleeve into the cavityof the bit body.

Embodiment 18: The method of any one of Embodiments 14 through 17,further comprising selecting the replacement sleeve according to one ormore of a downhole subterranean earth formation, drilling fluidcomposition, and a drilling fluid flow rate expected during operation ofthe coring tool.

Embodiment 19: The method of any one of Embodiments 13 through 18,wherein a total circumferential dimension of the at least one facedischarge channel subtends an angle of at least about 108 degrees abouta longitudinal axis of the bit body in a plane transverse to thelongitudinal axis of the bit body 10.

Embodiment 20: The method of Embodiment 13, further comprising: formingan additional face discharge channel in an inner surface in the bit bodyafter removing the sleeve by one or more of a cutting, milling, turning,grinding, eroding, polishing, additive manufacturing, 3D printing, andcasting process; and installing a replacement sleeve into the cavity ofthe bit body, wherein the replacement sleeve is one of a repaired sleeveand a new sleeve.

While certain illustrative embodiments have been described in connectionwith the Figures, those of ordinary skill in the art will recognize andappreciate that the scope of this disclosure is not limited to thoseembodiments explicitly shown and described herein. Rather, manyadditions, deletions, and modifications to the embodiments describedherein may be made to produce embodiments within the scope of thisdisclosure, such as those hereinafter claimed, including legalequivalents. In addition, features from one disclosed embodiment may becombined with features of another disclosed embodiment while still beingwithin the scope of this disclosure, as contemplated by the inventors.

What is claimed is:
 1. A coring bit for use on a coring tool forextracting a sample of subterranean formation from a well bore,comprising: a bit body having a cavity, wherein a throat portion of thecavity extends into the bit body from a face of the bit body; and asleeve disposed within the cavity of the bit body, the sleeve configuredto separate at least one face discharge channel and a throat dischargechannel, the at least one face discharge channel located radiallyoutward of the sleeve, the throat discharge channel located radiallyinward of the sleeve.
 2. The coring bit of claim 1, further comprising acoring shoe disposed in the cavity of the bit body.
 3. The coring bit ofclaim 1, wherein the sleeve comprises two or more parts.
 4. The coringbit of claim 1, wherein the sleeve defines at least one recess in aradially inner surface of the sleeve, the at least one recess providingthe throat discharge channel with zones of higher and lower flowresistance.
 5. The coring bit of claim 1, wherein the throat dischargechannel comprises a first region and a second region, wherein the secondregion has a total flow area higher than a total flow area of the firstregion.
 6. The coring bit of claim 1, further comprising one or moreguide blocks affixed to an inner surface of the bit body within thecavity, the one or more guide blocks configured to guide the sleeve intoplace during insertion of the sleeve into the cavity of the bit body orto support the sleeve during operation of the coring bit.
 7. The coringbit of claim 1, wherein the sleeve defines one or more fluid passagesextending through the sleeve.
 8. The coring bit of claim 1, wherein atleast a portion of a length of the at least one face discharge channelhas non-circular cross-sectional shape.
 9. The coring bit of claim 8,wherein the portion of the length of the at least one face dischargechannel having a non-circular cross-sectional shape comprises about 40%or more of the length of the at least one face discharge channel. 10.The coring bit of claim 8, wherein a total circumferential dimension ofthe portion of the at least one face discharge channel subtends an angleof at least about 72 degrees about a longitudinal axis of the bit bodyin a plane transverse to the longitudinal axis of the bit body
 10. 11.The coring bit of claim 10, wherein a total circumferential dimension ofthe portion of the at least one face discharge channel subtends an angleof at least about 108 degrees about a longitudinal axis of the bit bodyin a plane transverse to the longitudinal axis of the bit body
 10. 12.The coring bit of claim 11, wherein a total circumferential dimension ofthe portion of the at least one face discharge channel subtends an angleof at least about 144 degrees about a longitudinal axis of the bit bodyin a plane transverse to the longitudinal axis of the bit body
 10. 13. Amethod of repairing a coring tool for extracting a sample ofsubterranean formation from a well bore, the method comprising: removinga sleeve from a cavity of a bit body of the coring tool, the sleeveconfigured to separate at least one face discharge channel and a throatdischarge channel during operation of the coring tool, the at least oneface discharge channel located radially outward of the sleeve, thethroat discharge channel located radially inward of the sleeve.
 14. Themethod of claim 13, further comprising: repairing a radially outersurface of the at least one face discharge channel after removing thesleeve; and installing a replacement sleeve into the cavity of the bitbody, wherein the replacement sleeve is one of the removed sleeve, arepaired sleeve, and a new sleeve.
 15. The method of claim 14, whereinrepairing the radially outer surface of the at least one face dischargechannel comprises forming at least a portion of the at least one facedischarge channel by one or more of a cutting, milling, turning,grinding, eroding, polishing, additive manufacturing, 3D printing, andcasting process.
 16. The method of claim 14, wherein the sleevecomprises two or more parts.
 17. The method of claim 14, furthercomprising installing at least one guide block in the cavity of the bitbody prior to installing the replacement sleeve into the cavity of thebit body.
 18. The method of claim 14, further comprising selecting thereplacement sleeve according to one or more of a downhole subterraneanearth formation, drilling fluid composition, and a drilling fluid flowrate expected during operation of the coring tool.
 19. The method ofclaim 13, wherein a total circumferential dimension of the at least oneface discharge channel subtends an angle of at least about 108 degreesabout a longitudinal axis of the bit body in a plane transverse to thelongitudinal axis of the bit body
 10. 20. The method of claim 13,further comprising: forming an additional face discharge channel in aninner surface in the bit body after removing the sleeve by one or moreof a cutting, milling, turning, grinding, eroding, polishing, additivemanufacturing, 3D printing, and casting process; and installing areplacement sleeve into the cavity of the bit body, wherein thereplacement sleeve is one of a repaired sleeve and a new sleeve.